Nearly all people who are employed in "white collar" (office) jobs spend more than half their waking hours seated. Ergonomists and doctors have found that poor sitting postures contribute significantly to back problems and that a worker who spends long hours leaning forward over a desk is subject to considerable strain on the muscles and other tissues of the back. Alleviating that strain requires frequent relaxation of the back muscles, which is best accomplished by leaning back from time to time to a relaxed or reclined posture. In a relaxed position, muscular exertion is reduced to a minimum. Actual observations by ergonomists have shown, in fact, that a seated person ordinarily changes position every eight to 10 minutes.
The fixed geometry of most institutional and office seating is poorly adapted to provide good support for the anatomical back of a seated person in other than a single position (if at all). Usually, such seating is designed to provide support for the anatomical back when the person sits upright. When the person leans back to a relaxed position, he normally slides forward on the seat and presses back against the seat back, but his middle back (in the area of the lower thoracic vertebrae and lumbar vertebrae) is largely unsupported in the relaxed posture, thus putting a different sort of strain on the back from the strain of sitting upright, but a strain nonetheless. A meaningful reduction of that strain requires that the anatomical middle back be supported in the relaxed position; only with such support can the strain of sitting upright be effectively relieved by leaning back from time to time.
The inventor of the present invention has previously made significant improvements in the comfort of institutional, contract and office chairs by mounting the seat on seat supports for backward and forward movement and mounting the back on back supports so that the back tilts backward from a resiliently restrained, relatively upright position. Chairs embodying those improvements, which are described and shown in U.S. Pat. Nos. 3,982,785 and 4,084,850, automatically change in geometry to conform to any of a range of sitting postures between sitting erect and reclining or stretching quite far backward and thus provide comfortable support throughout a wide range of sitting postures. Some of the chairs specifically described and shown in U.S. Pat. No. 4,084,850 are being marketed under the trademark "Vertebra" and have been widely acclaimed. The telescoping principle of mounting the seat disclosed in that patent has proven to be an effective, relatively low cost way of mounting the seat on a simple tubular frame member.
A very popular type of institutional chair which has been commercialized in a variety of forms uses a one-piece seat and back of molded fiberglass, plywood, metal or high-impact strength plastic mounted on legs, a pedestal or a beam (ganged seating). This type of seating is inexpensive, reasonably durable (in good quality forms), and fairly comfortable in the seating posture for which it was designed. It is, however, distinctly uncomfortable in other seating postures; the hard surface and fixed geometry do not permit one sitting in a chair of this type to be comfortably supported in, for example, a backwardly reclined position. Because people cannot sit in one position for long periods of time without tiring and relief of back strain requires good support of the back in the relaxed, leaning back posture, as discussed above, almost all institutional seating, the seating commonly used in auditoriums, conference rooms, and lecture rooms in schools, to name a few examples, produces fatigue and diminished alertness and attentiveness, the longer people sit in such seating.